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BACKGROUND

The definition of immune compromise is characterized by an impairment of a host’s ability to effectively handle infectious challenges. As new therapeutic options for previously untreatable illnesses become available, a growing number of children fall into this category. This chapter focuses primarily on the infection-related issues among children who are immunocompromised owing to solid organ or hematopoietic cell transplantation; splenic dysfunction will also be addressed. These special hosts may present for the evaluation of unexplained fever, or with focal signs of infection, and often require a different approach than pursued in an otherwise healthy child. The goal of this chapter is to provide the pediatric hospitalist with a framework for infectious diseases evaluation in these children. Infectious complications related to chemotherapy for malignancy are discussed in Chapter 133.

PATHOPHYSIOLOGY

Solid organ transplantation (SOT) was revolutionized in the early 1980s with the introduction of the immunosuppressant cyclosporine. Heart, kidney, liver, lung, and small bowel transplants have become acceptable therapies for end-organ disease. Although these procedures allow improved survival, infectious complications are among the leading causes of morbidity and mortality in the SOT population.1 While the surgical procedure itself carries risk of infection following SOT, the immunosuppressive medications used to avoid graft rejection pose significantly higher and more prolonged infectious risks for transplant recipients. The underlying medical conditions necessitating SOT also carry infectious risks that need to be considered. Patients with cystic fibrosis, for example, are colonized with pathogens in their sinuses and upper respiratory tracts which are not impacted by lung transplant. Patients with renal or liver failure, meanwhile, may be predisposed to infection prior to transplant owing to end-organ dysfunction.

Hematopoietic cell transplantation (HCT), which includes transplantation of marrow- or blood-derived stem cells derived from peripheral blood, umbilical cord blood, or bone marrow, treat certain malignancies, metabolic disorders, and immune dysfunctions. Advances in immunosuppression have dramatically improved survival in HCT, but have led to an increased risk of infectious complications. Despite preventive antimicrobial therapies, infection is a leading cause of morbidity and mortality in both autologous and allogeneic HCT recipients.

CLINICAL PRESENTATION

There are several important variables when evaluating transplant recipients with suspected infection: the type of transplant (type of organ; allogeneic vs. autologous HCT), the amount of time since transplantation (state of immunosuppression), the underlying disease (indication for transplantation), and the environment of the recipient. In solid organ transplantation, the type of organ transplanted confers different technical challenges. Understanding the basic anatomical considerations of organ transplantation facilitates diagnosis and guides empiric antimicrobial therapy during postoperative infections. In HCT, autologous transplants (cells derived from the patient) affords lower risk of infection than use of allogeneic, or donor-derived, cells. As will be discussed below under Differential Diagnosis, the time since transplantation is a critical component to assessing risk of infection in transplant recipients. The degree of immunosuppression varies over time and with it the ...

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